Path computation element protocol (PCEP) operations to support wavelength switched optical network routing, wavelength assignment, and impairment validation

ABSTRACT

An apparatus comprising a path computation element (PCE) configured for at least partial impairment aware routing and wavelength assignment (RWA) and to communicate with a path computation client (PCC) based on a PCE protocol (PCEP) that supports path routing, wavelength assignment (WA), and impairment validation (IV). The PCEP comprises at least one operation selected from the group consisting of a new RWA path request operation and a path re-optimization request operation. Also disclosed is a network component comprising at least one processor configured to implement a method comprising establishing a PCEP session with a PCC, receiving path computation information comprising RWA information and constraints from the PCC, and establishing impairment aware RWA (IA-RWA) based on the path computation information and a private impairment information for a vendor&#39;s equipment.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication Ser. No. 61/156,287 filed Feb. 27, 2009 by Young Lee, et al.and entitled “Path Computation Element System Architecture andFunctional Requirement to Support Wavelength Switched Optical NetworkRouting, Wavelength Assignment, and Impairment Validation,” which isincorporated herein by reference as if reproduced in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Wavelength division multiplexing (WDM) is one technology that isenvisioned to increase bandwidth capability and enable bidirectionalcommunications in optical networks. In WDM networks, multiple datasignals can be transmitted simultaneously between network elements (NEs)using a single fiber. Specifically, the individual signals may beassigned different transmission wavelengths so that they do notinterfere or collide with each other. The path that the signal takesthrough the network is referred to as the lightpath. One type of WDMnetwork, a wavelength switched optical network (WSON), seeks to switchthe optical signals with fewer optical-electrical-optical (OEO)conversions along the lightpath, e.g. at the individual NEs, thanexisting optical networks.

One of the challenges in implementing WDM networks is the determinationof the routing and wavelength assignment (RWA) during path computationfor the various signals that are being transported through the networkat any given time. Unlike traditional circuit-switched andconnection-oriented packet-switched networks that merely have todetermine a route for the data stream across the network, WDM networksare burdened with the additional constraint of having to ensure that thesame wavelength is not simultaneously used by two signals over a singlefiber. This constraint is compounded by the fact that WDM networkstypically use specific optical bands comprising a finite number ofusable optical wavelengths. As such, the RWA continues to be one of thechallenges in implementing WDM technology in optical networks.

Path computations can also be constrained due to other issues, such asexcessive optical noise, along the lightpath. An optical signal thatpropagates along a path may be altered by various physical processes inthe optical fibers and devices, which the signal encounters. When thealteration to the signal causes signal degradation, such physicalprocesses are referred to as “optical impairments.” Optical impairmentscan accumulate along the path traversed by the signal and should beconsidered during path selection in WSONs to ensure signal propagation,e.g. from an ingress point to an egress point, with acceptable amount ofdegradation.

SUMMARY

In one embodiment, the disclosure includes an apparatus comprising apath computation element (PCE) configured for at least partialimpairment aware routing and wavelength assignment (RWA) and tocommunicate with a path computation client (PCC) based on a PCE protocol(PCEP) that supports path routing, wavelength assignment (WA), andimpairment validation (IV). The PCEP includes at least one operationselected from the group consisting of a new RWA path request operationand a path re-optimization request operation.

In another embodiment, the disclosure includes a network componentcomprising at least one processor configured to implement a methodcomprising establishing a PCEP session with a PCC, receiving pathcomputation information comprising RWA information and constraints fromthe PCC, establishing impairment aware RWA (IA-RWA) based on the pathcomputation information and a private impairment information for avendor's equipment. The method performed by the network component alsoincludes selectively transmitting at least one of a new RWA path requestand a RWA path re-optimization request to the PCC.

In yet another embodiment, the disclosure includes a method comprisingestablishing impairment aware routing and wavelength assignment for aplurality of NEs in an optical network using routing and combined WA andIV. The method also includes performing at least one operation selectedfrom the group consisting of a new RWA path request operation and a pathre-optimization request operation.

These and other features will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is a schematic diagram of an embodiment of a WSON system.

FIG. 2 is a schematic diagram of an embodiment of a combined impairmentaware RWA architecture.

FIG. 3 is a schematic diagram of another embodiment of a combinedimpairment aware RWA architecture.

FIG. 4 is a schematic diagram of an embodiment of a separated impairmentaware RWA architecture.

FIG. 5 is a schematic diagram of another embodiment of a separatedimpairment aware RWA architecture.

FIG. 6 is a schematic diagram of another embodiment of a separatedimpairment aware RWA architecture.

FIG. 7 is a schematic diagram of another embodiment of a separatedimpairment aware RWA architecture.

FIG. 8 is a schematic diagram of an embodiment of a distributedimpairment aware RWA architecture.

FIG. 9 is a protocol diagram of an embodiment of a path computationcommunication method.

FIG. 10 is a protocol diagram of another embodiment of a pathcomputation communication method.

FIG. 11 is a protocol diagram of another embodiment of a pathcomputation communication method.

FIG. 12 is a schematic diagram of an embodiment of a general-purposecomputer system.

DETAILED DESCRIPTION

It should be understood at the outset that although an illustrativeimplementation of one or more embodiments are provided below, thedisclosed systems and/or methods may be implemented using any number oftechniques, whether currently known or in existence. The disclosureshould in no way be limited to the illustrative implementations,drawings, and techniques illustrated below, including the exemplarydesigns and implementations illustrated and described herein, but may bemodified within the scope of the appended claims along with their fullscope of equivalents.

To ensure proper operations in optical networks, a plurality of networkcomponents (e.g. NEs, subsystems, devices, cabling, etc.) may becharacterized at a detailed level. The detailed characteristics of suchnetwork components may be considered during network planning,installation, and turn-up phases. Additionally, the network componentcharacteristics may be used during day-to-day operations, such as forcomputing and establishing lightpaths and monitoring connections. Thedetailed characteristics may comprise optical impairment due to physicalprocesses in the components.

In a PCE-based Architecture, a PCE may compute Label Switched Paths(LSP) in Multiprotocol Label Switching Traffic Engineering (MPLS-TE) andGeneralized MPLS (GMPLS) networks at the request of PCCs. A PCC may beany network component that makes such a request and may be for instancean Optical Switching Element within a WDM network. The PCE, itself, maybe located anywhere within the network, and may be within an opticalswitching element, a Network Management System (NMS) or OperationalSupport System (OSS), or may be an independent network server.

PCEP is the communication protocol used between PCC and PCE, and mayalso be used between cooperating PCEs. Disclosed herein areapplication-specific requirements for PCEP for the support of WavelengthSwitched Optical Networks (WSONs). As used herein, each WSON refers to aWDM based optical network in which switching is performed selectivelybased on the wavelength of an optical signal. Lightpath provisioning inWSONs requires a RWA process. From a path computation perspective,wavelength assignment is the process of determining which wavelength canbe used on each hop of a path and forms an additional routing constraintto optical light path computation. Additionally, optical impairments mayadd further constraints on the paths available for use.

The paths in a WSON are referred to as lightpaths. Each lightpath mayspan multiple fiber links and each path should be assigned a wavelengthfor each link. A transparent optical network is made up of opticaldevices that can switch but not convert from one wavelength to another.In a transparent optical network, a lightpath operates on the samewavelength across all fiber links that it traverses. In such cases, thelightpath is said to satisfy the wavelength-continuity constraint. Twolightpaths that share a common fiber link can not be assigned the samewavelength. To do otherwise would result in both signals interferingwith each other. Note that additional multiplexing techniques such aspolarization based multiplexing are not addressed herein. Assigning theproper wavelength on a lightpath is an essential requirement in theoptical path computation process.

On the other hand, when a switching node has the ability to performwavelength conversion, the wavelength-continuity constraint can berelaxed, and a lightpath may use different wavelengths on differentlinks along its route from origin to destination. It is, however, to benoted that wavelength converters may be limited due to their relativelyhigh cost. The number of WDM channels that can be supported in a fiberis also limited. In accordance with at least some embodiments, a WSONmay be composed of network nodes that cannot perform wavelengthconversion, nodes with limited wavelength conversion, and nodes withfull wavelength conversion abilities. Accordingly, wavelength assignmentis an additional routing constraint to be considered in all lightpathcomputations.

Some optical sub-networks are designed such that over any path thedegradation to an optical signal due to impairments never exceedsprescribed bounds. This may be due to the limited geographic extent ofthe network, the network topology, and/or the quality of the fiber anddevices employed. In such networks, the path selection problem reducesto determining a continuous wavelength from source to destination (theRouting and Wavelength Assignment problem). In other optical networks,impairments are important and the path selection process must beimpairment-aware.

One of the most basic questions in communications is whether one cansuccessfully transmit information from a transmitter to a receiverwithin a prescribed error tolerance, usually specified as a maximumpermissible bit error ratio (BER). This generally depends on the natureof the signal transmitted between the sender and receiver and the natureof the communications channel between the sender and receiver. Theoptical path utilized (along with the wavelength) determines thecommunications channel.

The optical impairments incurred by the signal along the fiber and ateach optical network element along the path determine whether the BERperformance or any other measure of signal quality can be met for thisparticular signal on this particular path. Given the existing standardscovering optical characteristics (impairments) and the knowledge of howthe impact of impairments may be estimated along a path, a frameworkexists for impairment-aware path computation and establishment utilizingGMPLS protocols and the PCE architecture.

Some transparent optical sub-networks are designed such that over anypath the degradation to an optical signal due to impairments neverexceeds prescribed bounds. This may be due to the limited geographicextent of the network, the network topology, and/or the quality of thefiber and devices employed. In such network, the path selection problemreduces to determining a continuous wavelength from source todestination (the Routing and Wavelength Assignment problem). In otheroptical networks, impairments are important and the path selectionprocess must be impairment-aware.

Disclosed herein are processes for routing and wavelength assignment(RWA) used when wavelength continuity constraints are present. Theseprocesses are reviewed for optical impairment aware RWA (IA-RWA). Basedon selected process models, PCEP requirements are specified to supportIA-RWA.

In accordance with at least some embodiments, three alternative processarchitectures are given for performing routing and wavelength assignment(RWA). The process architectures are referred to herein as “combinedRWA,” “separated RWA,” and “distributed RWA.” These alternative processarchitectures have the following properties and impact PCEP requirementsin different ways. For combined RWA, path selection and wavelengthassignment are performed as a single process. The requirements forPCC-PCE interaction with such a combined RWA process PCE is addressedherein. For separated RWA, the routing process furnishes one or morepotential paths to the wavelength assignment process that then performsfinal path selection and wavelength assignment. The requirements forPCE-PCE interaction with one PCE implementing the routing process andanother implementing the wavelength assignment process is not addressedherein. For distributed RWA, a standard path computation (unaware ofdetailed wavelength availability) takes place, and then wavelengthassignment is performed along this path in a distributed manner viasignaling (e.g. resource reservation protocol traffic engineering(RSVP-TE)). This alternative should be covered by existing or emergingGMPLS PCEP extensions and does not present new WSON specificrequirements.

In accordance with at least some embodiments, impairments in RWAarchitectures are addressed by adding an IV process. Such RWAarchitectures with IV are referred to herein as impairment-aware(IA)-RWAs. More specifically, three alternative architectures of RWAswith an IV process are referred to herein as “combined IA-RWA,”“separated IA-RWA,” and “distributed IA-RWA” architectures. Thesealternative IA-RWAs have the following properties and impact on PCEPrequirements. For combined IA-RWA, the processes of impairmentvalidation, routing, and wavelength assignment are aggregated into asingle PCE. The requirements for PCC-PCE interaction with the combinedIA-RWA architecture are addressed herein. For separated IA-RWA, theimpairment validation process may be separated from the RWA process todeal with impairment sharing constraints. For example, one PCE maycompute impairment candidates and another PCE uses this informationwhile performing RWA. The requirements for PCE-to-PCE interaction withthe separated IA-RWA architecture are addressed herein. In distributedIA-RWA, a standard path computation (unaware of detailed wavelengthavailability or optical impairments) takes place. Then, wavelengthassignment and impairment validation is performed along this path in adistributed manner via signaling (RSVP-TE). PCEP requirements for thedistributed IA-RWA architecture may be covered by existing or emergingGMPLS PCEP extensions and does not present new WSON specificrequirements.

The RWA and IA-RWA architectures described herein may be reduced to twoPCE-based implementations. In a first PCE-based implementation, theprocesses of routing, wavelength assignment and impairment validationare accessed via a single PCE. In this first PCE-based implementation,the details of the interactions of the processes are not subject tostandardization, but the PCC to PCE communications are subject tostandardization. In a second PCE-based implementation, the impairmentvalidation process is implemented in a separate PCE. In this secondPCE-based implementation, the RWA-PCE acts as a coordinator and the PCCto RWA-PCE interface will be the same as for the first PCE-basedimplementation. However, in the second PCE-based implementation, thereare additional requirements for the RWA-PCE to IV-PCE interface.

Several new PCEP operations for RWA architectures are possible. Forexample, an RWA-PCC to PCE interface may perform several operationsincluding a new RWA path request/reply, an RWA path re-optimizationrequest/reply, and a combined primary and backup RWA request. For thenew RWA path request, the Path Computation Request (PCReq) Messageincludes the path computation type (e.g., RWA or only routing). Thisrequirement is needed to differentiate between routing with thedistribute wavelength assignment option and combined RWA. Further, thePCReq Message may include optical signal quality parameters to which allfeasible paths should conform. Examples of the optical signal qualityparameters include, but are not limited to, the BER limit, the Q factor,optical signal to noise ratio (OSNR)+Margin, and polarization modedispersion (PMD). As used herein, “margin” corresponds to an “insurance”(e.g. 3˜6 dB) for suppliers and operators against unpredictabledegradation and unestimatable degradation due to fiber nonlinearity andmismatched wavelength along the path. If the PCReq Message does notinclude the BER limit and no default BER limit is provisioned at thePCE, then the PCE will return an error specifying that a BER limit mustbe provided.

Further, the PCReq Message for a new RWA path request includes theroute, wavelengths assigned to the route, and an indicator regardingwhether the path conforms to an optical quality threshold or not. In thecase where a valid path is not found, the Path Computation Reply (PCRep)Message includes information regarding why the path is not found (e.g.,no route, wavelength not found, BER failure, etc.)

For the RWA path re-optimization request, the PCReq Message provides thepath to be re-optimized and include the following options: (1)re-optimize the path keeping the same wavelength(s); (2) re-optimizewavelength(s) keeping the same path; and (3) re-optimize allowing bothwavelength and the path to change. The corresponding PCRep Message forthe re-optimized request provides the re-optimized path and wavelengths.If a BER limit is provided in the original new RWA path request then aBER limit is furnished in the re-optimization request. Otherwise,furnishing a BER limit is optional. In the case where the path is notfound, the PCRep Message includes information regarding why the path isnot found (e.g., no route, wavelength not found, both route andwavelength not found, etc.).

For the combined primary and backup RWA request, the PCReq Messageincludes the wavelength usage options: (1) the same wavelength isrequired for the primary and backup paths; and (2) different wavelengthsfor primary and backup paths are permitted. For at least some PCEoperations, any PCReq Message that is associated with a request forwavelength assignment also specifies restrictions on the wavelengths tobe used. However, the requestor (PCC) is not required to furnish anyrange restrictions. Such restrictions may be interpreted by the PCE as aconstraint on the tuning ability of the origination laser transmitter.

For a RWA-PCE to IV-PCE interface, various new PCEP considerations forthe interface between the RWA-Coord-PCE and the IV-Candidates-PCE arespecified herein. For such an interface, the PCReq Message from theRWA-Coord-PCE to the IV-PCE includes an indicator that more than one(candidate) path between source and destination is desired. Further, thePCReq message from the RWA-Coord-PCE to the IV-Candidates-PCE includes alimit on the number of optical impairment qualified paths to be returnedby the IV-PCE. Further, the PCReq message from the RWA-Coord-PCE to theIV-Candidates-PCE may include wavelength constraints. Note that opticalimpairments are wavelength sensitive and hence specifying a wavelengthconstraint may help limit the search for valid paths. In addition, thePCRep Message from the IV-Candidates-PCE to RWA-Coord-PCE includes a setof optical impairment qualified paths along with any wavelengthconstraints on those paths. The PCRep Message from the IV-Candidates-PCEto RWA-Coord-PCE also indicates “no path found” in the case where avalid path is not found. The PCReq Message from the RWA-PCE to theIV-PCE may include one or more specified paths and wavelengths that areto be verified by the IV-PCE. This option is applicable, for example,when the IV-PCE is allowed to verify specific paths. Note that once thecombined RWA Process PCE receives the resulting paths from the IVCandidates' PCE, the Combined RWA PCE computes RWA for the IV qualifiedcandidate paths and sends the result back to the PCC.

In accordance with at least some embodiments, manageabilityconsiderations for WSON Routing and Wavelength Assignment (RWA) with PCEaddress the following issues: (1) control of function and policy; (2)information and data models (e.g., management information base (MIB)module); (3) liveness detection and monitoring; (4) verifying correctoperation; (5) requirements on other protocols and functionalcomponents; (6) impact on network operation.

With regard to issue one (control of function and policy), the PCEPimplementation disclosed herein should allow configuring PCEP sessionparameters on PCC including the ability to send a WSON RWA request.Further, the PCEP implementation should allow configuring PCEP sessionparameters on a PCE including support for WSON RWA and the maximumnumber of synchronized path requests associated with a WSON RWA perrequest message. Further, the PCEP implementation provides a set of WSONRWA specific policy parameters (e.g., authorized sender, request ratelimiter, etc). Such parameters may be configured as default parametersfor any PCEP session the PCEP speaker participates in, or may apply to aspecific session with a given PCEP peer or a specific group of sessionswith a specific group of PCEP peers.

With regard to issue two (information and data models), the PCEPimplementation disclosed herein defines extensions to the PCEP MIBmodule to cover new PCEP operations and parameters. With regard to issuethree (liveness detection and monitoring), the PCEP implementationdisclosed herein does not imply any new liveness detection andmonitoring requirements compared to previous PCEP implementations. Withregard to issue four (verifying correct operation), the PCEPimplementation disclosed herein does not imply any new verificationrequirements compared to previous PCEP implementations. With regard toissue five (requirements on other protocols and functional components),the PCEP implementation disclosed herein may be used with existing PCEdiscovery mechanisms to advertise WSON RWA path computation capabilitiesto PCCs. With regard to issue six (impact on network operation), thePCEP implementation disclosed herein does not imply any new networkoperation requirements compared to previous PCEP implementations.

FIG. 1 illustrates one embodiment of a WSON system 100. In accordancewith embodiments, the WSON system 100 is supported by theapplication-specific requirements for PCEP as described herein. Thesystem 100 may comprise a WSON 110, a control plane controller 120, anda PCE 130. The WSON 110, control plane controller 120, and PCE 130 maycommunicate with each other via optical, electrical, or wireless means.The WSON 110 may comprise a plurality of NEs 112 coupled to one anotherusing optical fibers. In an embodiment, the optical fibers may also beconsidered NEs 112. The optical signals may be transported through theWSON 110 over lightpaths that may pass through some of the NEs 112. Inaddition, some of the NEs 112, for example those at the ends of the WSON110, may be configured to convert between electrical signals fromexternal sources and the optical signals used in the WSON 110. Althoughfour NEs 112 are shown in the WSON 110, the WSON 110 may comprise anyquantity of NEs 112.

The WSON 110 may be any optical network that uses active or passivecomponents to transport optical signals. The WSON 110 may implement WDMto transport the optical signals through the WSON 110, and may comprisevarious optical components as described in detail below. The WSON 110may be part of a long haul network, a metropolitan network, or aresidential access network.

The NEs 112 may be any devices or components that transport signalsthrough the WSON 110. In an embodiment, the NEs 112 consist essentiallyof optical processing components, such as line ports, add ports, dropports, transmitters, receivers, amplifiers, optical taps, and so forth,and do not contain any electrical processing components. Alternatively,the NEs 112 may comprise a combination of optical processing componentsand electrical processing components. At least some of the NEs 112 maybe configured with wavelength converters, optical-electrical (OE)converters, electrical-optical (EO) converters, OEO converters, orcombinations thereof. However, it may be advantageous for at least someof the NEs 112 to lack such converters as such may reduce the cost andcomplexity of the WSON 110. In specific embodiments, the NEs 112 maycomprise optical cross connects (OXCs), photonic cross connects (PXCs),optical add/drop multiplexers (OADMs), type I or type II reconfigurableoptical add/drop multiplexers (ROADMs), wavelength selective switches(WSSs), fixed optical add/drop multiplexers (FOADMs), or combinationsthereof.

The NEs 112 may be coupled to each other via optical fibers. The opticalfibers may be used to establish optical links and transport the opticalsignals between the NEs 112. The optical fibers may comprise standardsingle mode fibers (SMFs) as defined in the InternationalTelecommunication Union (ITU) Telecommunication Standardization Sector(ITU-T) standard G.652, dispersion shifted SMFs as defined in ITU-Tstandard G.653, cut-off shifted SMFs as defined in ITU-T standard G.654,non-zero dispersion shifted SMFs as defined in ITU-T standard G.655,wideband non-zero dispersion shifted SMFs as defined in ITU-T standardG.656, or combinations thereof. These fiber types may be differentiatedby their optical impairment characteristics, such as attenuation,chromatic dispersion, polarization mode dispersion, four wave mixing, orcombinations thereof. These effects may be dependent upon wavelength,channel spacing, input power level, or combinations thereof. The opticalfibers may be used to transport WDM signals, such as course WDM (CWDM)signals as defined in ITU-T G.694.2 or dense WDM (DWDM) signals asdefined in ITU-T G.694.1. All of the standards described herein areincorporated herein by reference. The network layer where the NEs 112operate and communicate may be referred to as the transport plane.

The control plane controller 120 may coordinate activities within theWSON 110. Specifically, the control plane controller 120 may receiveoptical connection requests and provide lightpath signaling to the WSON110 via Multiprotocol Label Switching Traffic Engineering (MPLS-TE) orGMPLS, thereby coordinating the NEs 112 such that data signals arerouted through the WSON 110 with little or no contention. In addition,the control plane controller 120 may communicate with the PCE 130 usingPCEP to provide the PCE 130 with information that may be used for thepath computation, and/or receive the path computation from the PCE 130and forward the path computation to the NEs 112. The control planecontroller 120 may be located in a component outside of the WSON 110,such as an external server, or may be located in a component within theWSON 110, such as a NE 112. The network layer where the control planecontroller 120 operates may be referred to as the control plane, whichmay be separated from and may manage the transport plane.

The PCE 130 may perform all or part of the RWA for the WSON system 100,e.g. at the control plane. Specifically, the PCE 130 may receive thewavelength or other information that may be used for the RWA from thecontrol plane controller 120, from the NEs 112, or both. The PCE 130 mayprocess the information to obtain the RWA, for example by computing theroutes or lightpaths for the optical signals, specifying the opticalwavelengths that are used for each lightpath, and determining the NEs112 along the lightpath at which the optical signal should be convertedto an electrical signal or a different wavelength. The RWA may includeat least one route for each incoming signal and at least one wavelengthassociated with each route. The PCE 130 may then send all or part of theRWA information to the control plane controller 120 or directly to theNEs 112. To assist the PCE 130 in this process, the PCE 130 may comprisea global traffic-engineering database (TED), a RWA information database,an optical performance monitor (OPM), a physical layer constraint (PLC)information database, or combinations thereof. The PCE 130 may belocated in a component outside of the WSON 110, such as an externalserver, or may be located in a component within the WSON 110, such as aNE 112.

In some embodiments, the PCE 130 may receive a path computation requestfrom a PCC. The PCC may be any client application requesting a pathcomputation to be performed by the PCE 130. The PCC may also be anynetwork component that makes such a request, such as the control planecontroller 120, or any NE 112, such as a ROADM or a FOADM. Generally,the PCC communicates with the PCE 130 using PCEP, although otheracceptable communications protocol may be used as well.

There may be many types of path computation constraints that can affectthe path computation at the PCE 130. The patch computation constraintsmay be included in the path computation request by the PCC. In oneembodiment, the path computation constraints include optical qualityconstraints. Examples of such include the optical signal-to-noise ratio(OSNR), amplifier spontaneous emission (ASE), polarization modedispersion (PMD), polarization-dependent loss (PDL), coherent opticalcrosstalk, incoherent optical crosstalk, effective pass-band, gainnon-uniformity, gain transients, chromatic dispersion, or combinationsthereof. In some embodiments, the path computation constraints may beclassified as linear in that their effects are independent of theoptical signal power and they affect the wavelengths individually.Alternatively, the path computation constraints may be classified asnonlinear in that their effects are dependent of the optical signalpower, generate dispersion on a plurality of wavelength channels, inducecrosstalk between wavelength channels, or combinations thereof.Regardless, the path computation constraints may be communicated to thePCE 130 so that the PCE 130 may consider them when computing a signal'spath through the WSON 100.

The path computation information used in the WSON system 100 may alsocomprise impairment information, which may be used to perform IA-RWA inthe WSON 110. For instance, the PCE 130 may perform all or part of IVfor the WSON system 100, which may comprise validating a computed pathbased on any impairment in the path that may degrade a propagatedoptical signal. When optical impairments accumulate along a pathpropagated by an optical signal, the impairments may degrade the signal,which may decrease a bit error rate (BER) of the signal or even lead tofailure in detecting or demodulating the signal. The path may bevalidated if the BER of the signal (or any other measure of signalquality) due to optical impairments may be acceptable or tolerated andthe signal may be detected with sufficient accuracy. However, if the BERof the signal is substantially low due to optical impairments, the pathmay be rejected or excluded from the allowed paths.

The optical impairments may be influenced by physical processes orconditions of the network components, such as the type of fiber, thetypes and locations of NEs 112, the presence of other optical signalsthat may share a fiber segment along the signal's path, or combinationsthereof. The optical impairments and the physical processes that maycause such impairments are described in a plurality of opticalcommunications references, such as the Internet Engineering Task Force(IETF) Request for Comments (RFC) 4054, which is incorporated herein byreference as if reproduced in its entirety. Optical impairments are alsodescribed by Govind P. Agrawal in “Fiber-Optic Communications Systems,”published by Wiley-Interscience, 2002, and in “Nonlinear Fiber Optics,”published by Academic Press, 2007, both of which are incorporated hereinby reference.

Optical impairments may be ignored in some networks, where every pathmay be valid for the permitted signal types in the network. In thiscase, optical impairments may be considered during network design andthen ignored afterwards, e.g. during path computation. However, in othernetworks, e.g. larger networks, it may not be practical to limit theallowed paths for each signal type. Instead, IV may be performed for aplurality of paths using approximation techniques, such as link budgetsand dispersion (rise time) budgets, e.g. during path computation.Approximation techniques for IV are described in a plurality of opticalreferences, including ITU-T G.680 and ITU-T series G supplement 39(G.Sup39), both of which are incorporated herein by reference. Theapproximation techniques for IV may be based on impairment models andmay be used to approximate or estimate impairments due to networkcomponents (such as NEs), e.g. at the control plane level. For instance,approximated IV may comprise determining which paths may have anacceptable BER or OSNR for a signal type. In some cases, IA-RWA may beimproved in the network by combining approximated IV with RWA, e.g. at aPCE, as described below.

In some cases, impairment effects may require accurate estimation, suchas for the evaluation of impairment impact on existing paths prior tothe addition of a new path. A plurality of methods may be used foraccurate or detailed IV, such as methods based on solving a plurality ofpartial differential equations that describe signal propagation in afiber. The methods may also comprise using detailed models for thenetwork components. The estimation/simulation time of such methods maydepend on the situation or condition in the network. A significantamount of time may be needed to validate or qualify a path usingdetailed IV. To increase the probability of validating a path,approximated IV may be performed before the detailed IV. Since detailedIV may be based on estimation/simulation methods that may besubstantially different than the RWA methods, the detailed IV processmay be separated from the RWA process, e.g. using a separate IV entityor a separate PCE.

Some path computation information, such as RWA information, may beshared without restrictions or constraints between the path computationentities, e.g. between a PCE and a PCC or between PCEs. However, in somecases, the impairment information may be private information and may notbe shared between different vendors of different components in thenetwork. For instance, the impairment information may not be shared ifsome proprietary impairment models are used to validate paths or avendor chooses not to share impairment information for a set of NEs. Forexample, in a network that comprises a line segment that corresponds toa first vendor and traverses through a plurality of NEs (e.g. OADMs,PXCs, etc.) that correspond to a plurality of second vendors, theimpairment information for the line segment may be private and may notbe shared with the second vendors. However, the impairment informationfor the second vendors may be public and may be shared with the firstvendor.

In an embodiment, to maintain impairment information of a first vendorequipment private, the first vendor equipment may provide a list ofpotential paths to a first PCE in the network, which may consider thelist for path computation between an ingress node and an egress node.The list of paths may also comprise wavelength constraints and possiblyshared impairment information, e.g. for the first vendor and at least asecond vendor. The list may then be sent to a second PCE in the networkto perform IA-RWA. However, in relatively larger networks, the list ofpaths may be substantially large, which may cause scaling issues. Inanother embodiment, the first vendor equipment may comprise a PCE-likeentity that provides the list of paths to a PCE in the network in chargeof IA-RWA. The PCE-like entity may not perform RWA and therefore may notrequire knowledge of wavelength availability information. This approachmay reduce the scaling issues due to forwarding substantially largelists. In another embodiment, the first vendor equipment may comprise aPCE, which may be configured to perform IA-RWA, e.g. on behalf of thenetwork. This approach may be more difficult to implement than the otherapproaches but may reduce the amount of information exchanged and thequantity of path computation entities involved.

Further, a plurality of IV schemes may be used for IA-RWA, e.g. based ondifferent detail levels and/or different architectures. For instance,the IA-RWA process may comprise IV for candidate paths, where a set ofpaths (e.g. between two nodes) may be validated in terms of acceptableoptical impairment effects. Thus, the validated paths may be providedwith associated wavelength constraints. The paths and the associatedwavelengths may or may not be available in the network when provided,e.g. according to the current usage state in the network. The set ofpaths may be provided in response to a received request for at most K(where K is an integer) valid paths between two nodes. The set of pathsmay be provided without disclosing private impairment information abouta vendor's equipment. Additionally or alternatively, the IA-RWA processmay comprise detailed IV (IV-Detailed), where a validation request for apath and an associated wavelength may be submitted. The path and theassociated wavelength may then be validated and accordingly a responsemay be provided. Similar to the case of IV for candidate paths, the IVresponse may not disclose impairment information about the vendor'sequipment.

Alternatively, the IA-RWA process may comprise distributed IV, whereapproximated impairment degradation measures may be used, such as OSNR,differential group delay (DGD), etc. The approximated measures may becarried through and accumulated along a path, e.g. using GMPLS or othersignaling protocol. When the accumulated measures reach a destinationnode, a final decision may be made about the path validity. Thisapproach may require disclosing impairment information about a vendor'sequipment, e.g. along the path.

A plurality of IA-RWA architectures may be used in optical networks,e.g. WSONs, to perform routing, WA, and IV. FIG. 2 illustrates anembodiment of a combined IA-RWA architecture 200. For the combinedIA-RWA architecture 200, path selection and wavelength assignment arebased at least in part on new PCEP requirements such as the new RWA pathrequests, the RWA path re-optimization requests and/or the combinedprimary and backup RWA requests described herein.

In the combined IA-RWA architecture 200, a PCC 210 may send a pathcomputation request, which may comprise path computation information, toa PCE 220. The path computation request may comprise RWA information andthe PCE 220 may have previous knowledge of shared impairmentinformation, e.g. for a plurality of vendors' equipment. However, thePCE 220 may request additional impairment information, such asnon-shared impairment information for any additional vendor's equipment.The PCE 220 may then perform combined routing, WA, and IV using the RWAinformation and the impairment information. The PCE 220 may use a singlecomputation entity, such as a processor, to perform the combined IA-RWA.For example, the processor may process the RWA information and theimpairment information using a single or multiple algorithms to computethe lightpaths, to assign the optical wavelengths for each lightpath,and to validate the lightpaths. Alternatively, the PCE 220 may use aplurality of processors to compute and validate the lightpaths andassign the wavelengths.

During the IA-RWA process, the PCE 220 may perform approximated IV ordetailed IV to validate the lightpaths, as described above. Further, thePCE 220 may perform IV before RWA. As such, the PCE 220 may generatefirst a list of candidate and valid paths in terms of acceptableimpairment effects, and then perform RWA to provide computed paths basedon the list. Alternatively, the PCE 220 may perform RWA before IV, wherea list of computed paths may be first obtained and where then each pathmay be validated based on impairment information.

The amount of RWA information and impairment information needed by thePCE 220 to compute the paths may vary depending on the algorithm used.If desired, the PCE 220 may not compute the paths until sufficientnetwork links are established between the NEs or when sufficient RWAinformation and impairment information about the NEs and the networktopology is provided. The PCE 220 may then send the computed paths, andthe wavelengths assigned to the paths, to the PCC 210. The PCE responsemay not disclose impairment information about a vendor's equipment. Thecombined IA-RWA architecture 200 may improve the efficiency of IA-RWA,and may be preferable for network optimization, smaller WSONs, or both.

FIG. 3 illustrates an embodiment of another combined IA-RWA architecture300. For the combined IA-RWA architecture 300, path selection andwavelength assignment are based at least in part on new PCEPrequirements such as the new RWA path requests, the RWA pathre-optimization requests and/or the combined primary and backup RWArequests described herein.

In the combined IA-RWA architecture 300, a PCC 310 may send a pathcomputation request to a first PCE 320. The first PCE 320 may beconfigured to perform routing, WA, and IV for candidate paths(IV-Candidates). The first PCE 320 may use the RWA information in thepath computation request to perform a combined IA-RWA. The first PCE 320may have previous knowledge of shared impairment information for aplurality of vendors' equipment but may request additional impairmentinformation, such as non-shared impairment information for anyadditional vendor's equipment. The impairment information may comprise aset of K paths, e.g. between a source node and a destination node, and aplurality of wavelengths associated with the paths. The first PCE 320may generate a set of validated paths based on the impairmentinformation, e.g. using IV approximation techniques. The first PCE 320may perform RWA based on the generated set of validated paths. The firstPCE 320 may then send a list of computed and validated paths andassigned wavelengths to a second PCE (or IV entity), which may beconfigured to perform detailed IV (IV-Detailed).

The second PCE 322 may have previous knowledge of impairment informationthat may not be shared with the first PCE 320 and may use the impairmentinformation to validate the paths. Additionally, the second PCE 322 mayrequest additional impairment information, such as non-shared impairmentinformation for any additional vendor's equipment. Thus, the second PCE322 may validate each computed path and return a final list of validatedpaths to the first PCE 320, which may then forward the list to the PCC310. The final list of validated paths may not comprise the privateimpairment information.

In an alternative embodiment, the first PCE 320 may communicate with thesecond PCE 322 as many times as needed to check the validity of eachcomputed path. For instance, the first PCE 320 may send a validationrequest for each computed path to the second PCE 322, and the second PCE322 may return a positive or negative response for each request to thefirst PCE 320, based on the outcome of a detailed IV process. As such,the first PCE 320 may not obtain any private impairment information inthe response from the second PCE 322.

The combined IA-RWA architecture 300 may be used in the case where thefirst PCE 320, the second PCE 322, or both may access private impairmentinformation about a vendor's equipment but may not share it. Further,separating the IV process into an initial approximated IV and asubsequent detailed-IV between the first PCE 320 and the second PCE 322may improve the efficiency and precision of IA-RWA.

FIG. 4 illustrates an embodiment of a separated IA-RWA architecture 400.For the separated IA-RWA architecture 400, various new PCEPconsiderations for the interface between the RWA-Coord-PCE (PCE2 422 andPCE3 424) and the IV-PCE (PCE1 420) are specified. In at least someembodiments, the PCReq Message from the RWA-Coord-PCE (PCE2 422 and PCE3424) to the IV-PCE (PCE1 420) includes an indicator that more than one(candidate) path between source and destination is desired. Further, thePCReq message from the RWA-Coord-PCE (PCE2 422 and PCE3 424) to theIV-Candidates-PCE (PCE1 420) includes a limit on the number of opticalimpairment qualified paths to be returned by the IV-PCE (PCE1 420).Further, the PCReq message from the RWA-Coord-PCE (PCE2 422 and PCE3424) to the IV-Candidates-PCE (PCE1 420) may include wavelengthconstraints. Note that optical impairments are wavelength sensitive andhence specifying a wavelength constraint may help limit the search forvalid paths. Further, the PCRep Message from the IV-Candidates-PCE (PCE1420) to RWA-Coord-PCE includes a set of optical impairment qualifiedpaths along with any wavelength constraints on those paths. Further, thePCRep Message from the IV-Candidates-PCE (PCE2 422 and PCE3 424) toRWA-Coord-PCE (PCE1 420) indicates “no path found” in the case where avalid path is not found. Note that once the combined RWA Process PCE(PCE2 422 and PCE3 424) receives the resulting paths from the IVCandidates' PCE (PCE1 420), the combined RWA PCE (PCE2 422 and PCE3 424)computes RWA for the IV qualified candidate paths and sends the resultback to the PCC 410.

In the separated IA-RWA architecture 400, a PCC 410 may send a pathcomputation request to a first PCE (or IV entity) 420, which may beconfigured to perform IV using approximate or detailedtechniques/models. The first PCE 420 may have previous knowledge ofshared impairment information for a plurality of vendors' equipment butmay obtain additional impairment information, such as non-sharedimpairment information for any additional vendor's equipment. The firstPCE 420 may use the impairment information and possibly a set ofavailable wavelengths in the path computation request to generate a listof validated paths. For instance, the impairment information maycomprise a set of about K paths, e.g. between a source node and adestination node, and a plurality of wavelengths associated with thepaths. The first PCE 420 may generate a set of validated paths based onthe impairment information. The first PCE 420 may send the list of pathsand the associated wavelengths to the second PCE 422, e.g. withoutsharing the impairment information with the second PCE 422 or any otherPCE.

The second PCE 422 may be configured to assign wavelengths to the pathsprovided by the first PCE 420 and may then send the list of paths to athird PCE 424, which may be configured for routing assignments. Thethird PCE 424 may receive the path computation information from the PCC410 and perform path computation using the information from the PCC 410and the information from the first PCE 420 and second PCE 422 to obtaina plurality of computed and validated paths and correspondingwavelengths. The third PCE 424 may then send the computed paths andassigned wavelengths to the PCC 410.

In an alternative embodiment, the third PCE 424 may receive the pathcomputation request from the PCC 410 and generate a list of computedpaths and corresponding wavelengths, which may be sent to the second PCE422. The second PCE 422 may assign wavelengths to the paths andcommunicate the list of paths and wavelengths to the first PCE 420 tovalidate each path. For instance, the first PCE 420 may send a positiveor negative response for each computed path, e.g. without sharingprivate impairment information. Finally, the validated paths andassociated wavelengths may be sent to the PCC 410, via any of the PCEs.

FIG. 5 illustrates an embodiment of another separated IA-RWAarchitecture 500. For the separated IA-RWA architecture 500, new PCEPconsiderations for the interface between the RWA-Coord-PCE (PCE2 522)and the IV-PCE (PCE1 520) are specified. In at least some embodiments,the PCReq Message information described herein (e.g., for the separatedIA-RWA architecture 400) is passed between the RWA-Coord-PCE (PCE2 522)and the IV-PCE (PCE1 520) of the separated IA-RWA architecture 500.

In the separated IA-RWA architecture 500, a PCC 510 may send a pathcomputation request to a first PCE (or IV entity) 520, which may beconfigured to perform IV using approximate or detailed techniques/modelsand send a list of validated paths and corresponding wavelengths to asecond PCE 522, e.g. in a manner similar to the separated IA-RWAarchitecture 400. However, the second PCE 522 may be configured toperform combined RWA, e.g. using a shared processor or dedicatedprocessors. Thus, the second PCE 522 may receive the path computationinformation from the PCC 510 and perform path computation using theinformation from the PCC 510 and the information from the first PCE 520to obtain a plurality of computed and validated paths and correspondingwavelengths. The second PCE 522 may then send the computed paths andassigned wavelengths to the PCC 510. Separating the IV process and theRWA process between the first PCE 520 and the second PCE 522 may beadvantageous since the two different processes may be offloaded as suchto two separate and specialized processing entities, which may improvecomputation efficiency.

In an alternative embodiment, the second PCE 522 may receive the pathcomputation request from the PCC 510 and generate a list of computedpaths and corresponding wavelengths. The second PCE 522 may thencommunicate the list of paths and wavelengths to the first PCE 520 tovalidate each path. For instance, the first PCE 520 may send a positiveor negative response for each computed path, e.g. without sharingprivate impairment information. Finally, the validated paths andassociated wavelengths may be sent to the PCC 510, via any of the PCEs.

FIG. 6 illustrates an embodiment of another separated IA-RWAarchitecture 600. For the separated IA-RWA architecture 600, various newPCEP considerations for the interface between the RWA-Coord-PCE (PCE2622) and the IV-PCE (PCE1 620) are specified. In at least someembodiments, the PCReq Message information described herein (e.g., forthe separated IA-RWA architecture 400) is passed between RWA-Coord-PCE(PCE2 622) and the IV-PCE (PCE1 620) of the separated IA-RWAarchitecture 600.

In the separated IA-RWA architecture 600, a PCC 610 may send a pathcomputation request to a first PCE (or IV entity) 620, which may beconfigured to perform IV for candidate paths. The first PCE 620 may haveprevious knowledge of shared impairment information for a plurality ofvendors' equipment but may request additional impairment information,such as non-shared impairment information for any additional vendor'sequipment. The first PCE 620 may use the impairment information andpossibly a set of available wavelengths in the path computation requestto generate a list of validated paths. For instance, the impairmentinformation may comprise a set of about K paths, e.g. between a sourcenode and a destination node, and a plurality of wavelengths associatedwith the paths. The first PCE 620 may generate a set of validated pathsbased on the impairment information, e.g. using IV approximationtechniques. The first PCE 620 may send the list of paths and theassociated wavelengths to the second PCE 622. However, the first PCE 620may not share the impairment information with the second PCE 622.

The second PCE 622 may be configured to perform combined RWA, e.g. usinga shared processor or dedicated processors. The second PCE 622 mayreceive the path computation information from the PCC 610 and performpath computation using this information and the information from thefirst PCE 620 to obtain a plurality of computed and validated paths andcorresponding wavelengths. The second PCE 622 may then send a list ofcomputed and validated paths and assigned wavelengths to a third PCE (orIV entity) 624, which may be configured to perform detailed IV.

The third PCE 624 may have previous knowledge of impairment informationthat may not be shared with the second PCE 622 and may use theimpairment information to validate the paths. Additionally, the thirdPCE 624 may request additional impairment information, such asnon-shared impairment information for any additional vendor's equipment.Thus, the third PCE 624 may validate each computed path and return afinal list of validated paths to the second PCE 622. The second PCE 622or the first PCE 620 may then forward the final list to the PCC 610. Thefinal list of validated paths may not comprise the private impairmentinformation.

In an alternative embodiment, the second PCE 622 may communicate withthe third PCE 624 as many times as needed to check the validity of eachcomputed path. For instance, the second PCE 622 may send a validationrequest for each computed path to the third PCE 624, and the third PCE624 may return a positive or negative response to the second PCE 622,based on the outcome of a detailed IV process. As such, the second PCE622 may not obtain any private impairment information in the responsefrom the third PCE 624.

The combined IA-RWA architecture 600 may be used in the case where thefirst PCE 620 and/or the third PCE 624, but not the second PCE 622, mayaccess private impairment information about a vendor's equipment but maynot share it. Further, separating the IV process into an initialapproximated IV and a subsequent detailed IV between the first PCE 620and the third PCE 624 may improve the efficiency and precision ofIA-RWA.

FIG. 7 illustrates an embodiment of another separated IA-RWAarchitecture 700. For the separated IA-RWA architecture 700, various newPCEP considerations for the interface between the RWA-Coord-PCE (PCE2722) and the IV-PCE (PCE1 720) are specified. In at least someembodiments, the PCReq Message information described herein (e.g., forthe separated IA-RWA architecture 400) is passed between RWA-Coord-PCE(PCE2 722) and the IV-PCE (PCE1 720) of the separated IA-RWAarchitecture 700.

In the separated IA-RWA architecture 700, a PCC 710 may send a pathcomputation request to a first PCE 720, which may be configured forrouting assignments. The first PCE 720 may perform path computationusing path computation information from the PCC 710 and then send thecomputed paths and any RWA information in the path computation requestto the second PCE 722, which may be configured for combined WA and IV.

The second PCE 722 may receive the computed paths and RWA informationfrom the first PCE 720 and may have previous knowledge of sharedimpairment information, e.g. for a plurality of vendors' equipment. Thesecond PCE 722 may also request additional impairment information, suchas non-shared impairment information for any additional vendor'sequipment. Thus, the second PCE 722 may perform combined WA and IV usingthe RWA information and the impairment information. The second PCE 722may use a single, or a plurality of, processors to perform the combinedWA and IV. The second PCE 722 may perform approximated IV or detailed IVto validate the computed paths. Further, the second PCE 722 may performIV before WA. As such, the second PCE 722 may generate first a list ofcandidate and valid paths, e.g. based on the computed paths, and thenperform WA. Alternatively, the second PCE 722 may perform WA before IV,where wavelengths may be assigned to the computed paths and then eachpath may be validated based on impairment information. Since the IVprocess is wavelength dependent, combining WA and IV in the second PCE722 may improve the computation efficiency in the system. The final listof computed paths and assigned wavelengths may then be sent to the PCC710 via the second PCE 722 or the first PCE 720.

In an alternative embodiment, the second PCE 722 may receive the pathcomputation request from the PCC 710 and generate a list of validatedpaths and assigned wavelengths, which may be sent to the first PCE 720.The first PCE 720 may then compute a plurality of paths and associatedwavelengths based on the information from the first PCE 722. Finally,the computed and validated paths and associated wavelengths may be sentto the PCC 710, via any of the PCEs.

FIG. 8 illustrates an embodiment of a distributed IA-RWA architecture800. In the distributed IA-RWA architecture 800, a standard pathcomputation (unaware of detailed wavelength availability or opticalimpairments) takes place. Then, wavelength assignment and impairmentvalidation is performed along this path in a distributed manner viasignaling (RSVP-TE). New PCEP extensions for the distributed IA-RWAarchitecture 800 are not disclosed herein.

In the distributed IA-RWA architecture 800, a PCE 810 may receive someor all of the RWA information from the NEs 820, 830, and 840, perhapsvia direct link, and perform the routing assignment. The PCE 810 thendirectly or indirectly passes the routing assignment to the individualNEs 820, 830, and 840, which may then perform distributed WA and IV(WA/IV) at the local links between the NEs 820, 830, and 840, e.g. basedon local information.

For instance, the NE 820 may receive local RWA information from the NEs830 and 840 and send some or all of the RWA information to the PCE 810.The PCE 810 may compute the lightpaths using the received RWAinformation and send the list of lightpaths to the NE 820. The NE 820may use the list of lightpaths to identify the NE 830 as the next NE inthe lightpath. The NE 820 may establish a link to the NE 830, e.g. via asignaling protocol, and use the received local RWA information that maycomprise additional constraints to assign a wavelength for transmissionover the link. Additionally, the NE 820 may use local impairmentinformation to perform IV and generate a list of validated lightpaths.The list of validated paths may correspond to a plurality ofwavelengths, which may be specified by the PCE 810 or indicated in theRWA information. The NE 820 may perform approximated IV for at leastsome of the wavelengths based on approximated models and measures, whichmay be carried through and accumulated along a path, e.g. using GMPLS orGMPLS resource reservation protocol (RSVP). For example, the NE 820 mayperform IV based on a measure of signal quality, e.g. BER or OSNR, whichmay be accumulated along the path by the subsequent nodes.

The NE 830 may receive the list of lightpaths and the wavelengths fromthe NE 820, and use the list of lightpaths to identify the NE 840 as thenext NE in the lightpath. Hence, the NE 830 may establish a link to theNE 840 and assign the same or a different wavelength for transmissionover the link. The NE 830 may also use the same impairment informationused by the node 820 and/or other local impairment information toperform IV and update the list of validated lightpaths and theassociated wavelengths. The NE 830 may perform approximated IV based onthe same approximated models and measures (e.g. BER, OSNR, etc.), whichmay be updated and further accumulated by the node 830. Similarly, theNE 840 may receive the list of lightpaths and wavelengths from the NE830 and the impairment information, including the accumulated measures,from the node 840, update the received information, and propagate theinformation along the path.

Thus, the signals may be routed while the wavelengths are assigned andthe lightpaths are validated in a distributed manner between the NEsuntil a destination node is reached. Assigning the wavelengths at theindividual NEs may reduce the amount of RWA information and impairmentinformation that may be forwarded between the NEs and between the NEsand the PCE 810. However, such distributed WA/IV schemes may requiresharing some local and private impairment information between the NEs.Further, such signaling based schemes may become less practical as thequantity of computed paths and the available wavelengths increase.

At least some of the IA-RWA architectures described above may requirechanges in current protocols and/or standards, for example regarding thePCE, signaling, the information model, routing, or combinations thereof.Table 1 illustrates some aspects of the system that may require changesto support the IA-RWA architectures above.

TABLE 1 System aspects that may require changes for different IA-RWAarchitectures. Infor- Sig- mation IA-RWA Architecture PCE naling ModelRouting Combined IA-RWA architectures 200 Yes No Yes Yes Combined IA-RWAarchitectures 300 Yes No Yes Yes Combined IA-RWA architectures 400 No NoYes Yes Combined IA-RWA architectures 500 No No Yes Yes Combined IA-RWAarchitectures 600 No No Yes Yes Combined IA-RWA architectures 700 No NoYes Yes Combined IA-RWA architectures 800 No Yes Yes No

Some of the impairment models, which may be used in the IA-RWAarchitectures above, may be described in ITU-T G.680. ITU-T G.680includes some detailed and approximate impairment characteristics forfibers and various devices and subsystems. ITU-T G.680 also describes anintegrated impairment model, which may be used to support IA-RWA, e.g.in the architectures above. However, the impairment characteristics andmodels in ITU-T G.680 are suitable for a network that comprises a linesegment for a first vendor, which passes through a plurality of NEs(e.g. OADMs, PXCs, etc.) for a plurality of second vendors. Theimpairment information for the line segment may be private and theimpairment information for the second vendors may be public. However,additional or different impairment models and impairment characteristicsmay be required for other network configurations, where a plurality ofline segments or systems that correspond to a plurality of vendors maybe deployed across the system.

For instance, in the case of a distributed IA-RWA architecture, such asthe distributed IA-RWA architecture 800, an impairment information modeland an impairment “computation model” may be needed to enable IV.Further, the accumulated impairment measures, which may be propagatedand updated at a plurality of nodes along a path, may requirestandardization so that different nodes for different vendors in thesame system may support IV. ITU-T G.680 may describe some impairmentmeasures that may be used, such as computation formulas for OSNR,residual dispersion, polarization mode dispersion/polarization dependentloss, effects of channel uniformity, etc. However, ITU-T G.680 does notspecify which measurements may be stored or maintained in the nodes andin what form.

The different IA-RWA architectures above may also use differentpath/wavelength impairment validation, which may impose differentdemands on routing. For instance, in the case where approximateimpairment information is used to validate the paths, GMPLS routing maybe used to distribute the impairment characteristics of the NEs and thelinks, e.g. based on an impairment information model. In the case of adistributed IA-RWA architecture, no changes to the routing protocol maybe necessary, but substantial changes may be needed in the signalingprotocol to enable IV. For instance, the characteristics of thetransported signal in the distributed scheme, such as the signalmodulation type, may affect system tolerance to optical impairments.Therefore, it may be advantageous to communicate such signalcharacteristics in the distributed scheme, e.g. via signaling.

Further, the different IA-RWA architectures above may comprise differentPCE configurations, which may depend on the specific functionalitiesrequired for each architecture. For instance, in the case of thecombined IA-RWA architecture 200, a single PCE (e.g. PCE 220) mayperform all the computations needed for IA-RWA. As such, the PCE may beconfigured to maintain, e.g. in a TED, information about network (e.g.WSON) topology and switching capabilities, network WDM link wavelengthutilization, and network impairment information. The PCE may also beconfigured to receive a path computation request from a PCC that maycomprise a source node, a destination node, and a signal characteristic,type, and/or required quality. If the path computation is successful,the PCE may send a reply (or response) to the PCC that may comprise thecomputed path(s) and the assigned wavelength(s). Otherwise, if the pathcomputation is not successful, the PCE may send a response to the PCCthat indicates the reason that the path computation failed. For example,the response may indicate that the path computation failed due to lackof available wavelengths, due to impairment considerations, or both.

In the case of the separate IA-RWA architectures, such as the separateIA-RWA architecture 500, at least two PCEs (e.g. the PCE 520 and PCE522) may perform the IV and RWA separately. One of the PCEs (e.g. PCE522) may be configured to perform RWA computations and coordinate theoverall IA-RWA process and the other PCE (e.g. PCE 520) may beconfigured to perform IV for candidate paths (IV-Candidate). The RWA PCEmay interact with a PCC to receive path computation requests and withthe IV-Candidates PCE to perform IV as needed and obtain a valid set ofpaths and wavelengths. The RWA PCE may also be configured to maintain,e.g. in a TED, information about network (e.g. WSON) topology andswitching capabilities and about network WDM link wavelengthutilization. However, the IV RWA PCE may not maintain impairmentinformation.

The RWA PCE may also be configured to receive a path computation requestfrom a PCC that may comprise a source node, a destination node, and asignal characteristic, type, and/or required quality. If the pathcomputation is successful, the RWA PCE may send a reply (or response) tothe PCC that may comprise the computed path(s) and the assignedwavelength(s). Otherwise, if the path computation is not successful, theRWA PCE may send a response to the PCC that indicates the reason thatthe path computation had failed. For example, the response may indicatethat the path computation had failed due to lack of availablewavelengths, due to impairment considerations, or both. Additionally,the RWA PCE may be configured to send a request to the IV-Candidates PCEto ask for K paths and acceptable wavelengths for the paths between thesource node and the destination node in the PCC request. Accordingly,the RWA PCE may receive a reply (or response) from the IV-CandidatesPCE, which may comprise at most K requested paths and associatedwavelengths between the two nodes.

The IV-Candidates PCE may be configured for impairment aware pathcomputation without necessarily the knowledge of current link wavelengthutilization. The IV-Candidates PCE may interact with the RWA PCE, butnot with the PCC, and may maintain, e.g. in a TED, information aboutnetwork (e.g. WSON) topology and switching capabilities and networkimpairment information. However, the IV-Candidates PCE may not maintainnetwork WDM link wavelength utilization. The combined IA-RWAarchitecture 400 is another IA-RWA architecture that may comprise asimilarly configured IV-Candidates PCE.

Additionally or alternatively, one of the PCEs may be configured toperform detailed IV (IV-Detailed), such as in the separate IA-RWAarchitecture 600. The IV-Detailed PCE may maintain, e.g. in a TED,network impairment information and possibly information about WDM linkwavelength utilization. To coordinate overall IA-RWA, the RWA PCE maysend an IV request to the IV-Detailed PCE, which may comprise a list ofpaths and wavelengths and any signal characteristics and qualityrequirements. Thus, the IV-Detailed PCE may send back a reply (response)to the RWA PCE, which indicates whether the IV request wassuccessfully/unsuccessfully met. For example, the reply may indicate apositive/negative decision (e.g. yes/no decision). If the IV request isnot met, the IV-Detailed PCE may send a reply to the RWA PCE thatindicates the reason that the IV request failed. Consequently, the RWAPCE may determine whether to try a different signal, e.g. by modifying asignal parameter or characteristic. The combined IA-RWA architecture 300is another IA-RWA architecture that may comprise a similarly configuredIV-Detailed PCE.

FIG. 9 illustrates an embodiment of a path computation communicationmethod 900 between a PCC and a PCE. The PCE may be configured forcombined IA-RWA, such as in combined IA-RWA architecture 200. The method900 may be implemented using any suitable protocol including, but notlimited to, the new PCEP operations disclosed herein. In the method 900,the PCC may send a path computation request 902 to the PCE. The requestmay comprise path computation information and path computationconstraints. For example, the path computation information may compriseRWA information, including wavelength constraints, and possibly requiredimpairment information. At 904, the PCE calculates a path through thenetwork, which may be based on the path computation information and meetthe path computation constraints. For example, the PCE may perform RWAand IV based on the RWA information and the impairment information. ThePCE may then send a path computation reply 906 to the PCC. The reply 906may comprise the IA-RWA.

FIG. 10 illustrates an embodiment of a path computation communicationmethod 1000 between a PCC and at least two PCEs or computation entities.The two PCEs may be configured for separate RWA and IV, such as in theseparate IA-RWA architecture 500 and the separate IA-RWA architecture400. The method 1000 may be implemented using any suitable protocol,including, but not limited to, the new PCEP operations disclosed herein.In the method 1000, the PCC may send a path computation request 1002 tothe RWA PCE. The request may comprise path computation information andpath computation constraints. For example, the path computationinformation may comprise RWA information, including wavelengthconstraints. The path computation constraints may comprise qualityconstraints, e.g. between a first node (source node) and a second node(destination node), for a signal that may be represented by a specifiedtype (or a class) and associated parameters. The RWA PCE may send an IVrequest 1004 to the IV PCE, which may be an IV-Candidates PCE. As such,the RWA PCE may ask for K paths and acceptable wavelengths for the pathsbetween the two nodes indicated in the PCC request.

At 1006, the IV-Candidates PCE may perform IV, e.g. using approximatetechniques/models, to obtain a list of validated paths and associatedwavelengths. The IV-Candidates PCE may then send a reply 1008, whichcomprises the list of paths and wavelengths, to the RWA PCE. At 1010,the RWA PCE may perform RWA using the information from the IV-CandidatesPCE and the received path computation information/constraints. The RWAPCE may then send a path computation reply 1012 to the PCC, which maycomprise the IA-RWA.

FIG. 11 illustrates an embodiment of a path computation communicationmethod 1100 between a PCC and a plurality of PCEs or computationentities. The PCEs may be configured for separate RWA and IV-Candidatesand IV-Detailed processes, such as in the separate IA-RWA architecture600 and the combined IA-RWA architecture 300. The method 1100 may beimplemented using any suitable protocol including, but not limited to,the new PCEP operations disclosed herein. In the method 1100, the steps1102, 1104, 1106, 1108, and 1110 between the PCC, the RWA PCE, and theIV-Candidates PCE may be configured substantially similar to thecorresponding steps in the method 1000.

In step 1110 of the method 1100, the RWA PCE obtains the IA-RWAcalculations. However, before sending the IA-RWA to the PCC, the PC RWAmay send an IV request 1112 to the IV-Detailed PCE. As such, the RWA PCEmay request a detailed verification of the calculated paths and assignedwavelengths from the IV-Detailed PCE. At 1114, the IV-Detailed PCE mayperform IV, e.g. using detailed techniques/models, to validate thecomputed paths and corresponding wavelengths. The IV-Detailed PCE maythen send a reply 1116 to the RWA PCE, to confirm or reject eachcomputed path. The RWA PCE may update the list of paths and wavelengthsbased on the reply from the IV-Detailed PCE and then send a reply 1118to the PCC, which may comprise the final IA-RWA.

When a network comprises a plurality of PCEs, not all the PCEs withinthe network may have the ability to perform IA-RWA or RWA. Therefore,the network may comprise a discovery mechanism that allows the PCC todetermine the PCE in which to send the request, e.g. request 902, 1002,or 1102. For example, the discovery mechanism may comprise anadvertisement from a PCC for an IA-RWA capable PCE or RWA capable PCE,and a response from the PCEs indicating whether they have suchcapability. The discovery mechanism may be implemented as part of themethods 900, 1000, and 1100 or as a separate process.

The network components described above may be implemented on anygeneral-purpose network component, such as a computer or networkcomponent with sufficient processing power, memory resources, andnetwork throughput capability to handle the necessary workload placedupon it. FIG. 12 illustrates a typical, general-purpose networkcomponent suitable for implementing one or more embodiments of thecomponents disclosed herein. The network component 1200 includes aprocessor 1202 (which may be referred to as a central processor unit orCPU) that is in communication with memory devices including secondarystorage 1204, read only memory (ROM) 1206, random access memory (RAM)1208, input/output (I/O) devices 1210, and network connectivity devices1212. The processor may be implemented as one or more CPU chips, or maybe part of one or more application specific integrated circuits (ASICs).

The secondary storage 1204 is typically comprised of one or more diskdrives or tape drives and is used for non-volatile storage of data andas an over-flow data storage device if RAM 1208 is not large enough tohold all working data. Secondary storage 1204 may be used to storeprograms that are loaded into RAM 1208 when such programs are selectedfor execution. The ROM 1206 is used to store instructions and perhapsdata that are read during program execution. ROM 1206 is a non-volatilememory device that typically has a small memory capacity relative to thelarger memory capacity of secondary storage 1204. The RAM 1208 is usedto store volatile data and perhaps to store instructions. Access to bothROM 1206 and RAM 1208 is typically faster than to secondary storage1204.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods might beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

1. An apparatus comprising: a path computation element (PCE) configuredfor at least partial impairment aware routing and wavelength assignment(RWA) and to communicate with a path computation client (PCC) based on aPCE protocol (PCEP) that supports path routing, wavelength assignment(WA), and impairment validation (IV), wherein the PCEP comprises a PathComputation Request (PCReq) Message from a PCC to the PCE that initiatesat least one operation selected from the group consisting of a new RWApath request operation and a path re-optimization request operation,wherein the PCReq Message comprises at least one optical signal qualityparameter that indicates an impairment constraint that a computed pathmust meet to pass an impairment validation optical quality check, andwherein the PCC does not comprise and is not positioned in a networkmanagement system.
 2. The apparatus of claim 1, wherein the PCReqMessage initiates the new RWA path request operation and designates apath computation type as either RWA or routing only.
 3. The apparatus ofclaim 1, wherein the at least one optical signal quality parameter isselected from the group consisting of a bit error ratio (BER) limit, a Qfactor, optical signal to noise ratio (OSNR)+Margin, and polarizationmode dispersion (PMD).
 4. The apparatus of claim 2, wherein the PCEPfurther comprises a Path Computation Reply (PCRep) Message sent from thePCE to the PCC, and wherein the PCRep comprises a path route,wavelengths assigned to the route, and an indicator regarding whether apath has passed the optical quality check.
 5. The apparatus of claim 1,wherein, if a valid path is not found, the PCEP further comprises aPCRep Message, and wherein the PCRep Message comprises informationregarding why the path is not found.
 6. The apparatus of claim 1,wherein the PCReq Message initiates the RWA path re-optimization requestoperation, and wherein the PCReq Message indicates a path to bere-optimized and a re-optimization option.
 7. The apparatus of claim 6,wherein the re-optimization option indicates the path should bere-optimized by: re-optimizing the path while keeping the samewavelength(s); re-optimizing wavelength(s) while keeping the same path;or re-optimizing by allowing both wavelength and the path to change. 8.The apparatus of claim 1, wherein the PCEP comprises a combined primaryand backup RWA request operation which comprises the PCReq Message,wherein the PCReq Message comprises wavelength usage options, whereinthe wavelength usage options indicate a same wavelength is required forprimary and backup paths or different wavelengths for primary and backuppaths are permitted.
 9. The apparatus of claim 1, wherein the PCEPrequires any PCReq Message that is associated with a request forwavelength assignment to specify range restrictions on wavelengths to beused.
 10. The apparatus of claim 1 further comprising a RWA-PCE toIV-PCE interface, wherein the PCE is a RWA-PCE, wherein the PCEP causestransmission of a PCReq Message from the PCE to a IV-PCE, and whereinthe PCReq Message comprises an indicator that more than one candidatepath between source and destination is requested.
 11. The apparatus ofclaim 10, wherein the PCReq Message further indicates a limit on thenumber of optical impairment qualified paths to be returned by theIV-PCE.
 12. A network component comprising: a first path computationelement (PCE) configured for at least partial impairment aware routingand wavelength assignment (IA-RWA) and communication with a pathcomputation client (PCC) based on a PCE protocol (PCEP) that supportspath routing, wavelength assignment (WA), and impairment validation(IV), wherein the first PCE establishes a PCEP session with the PCC,wherein the first PCE receives a PCEP Path Computation Request (PCReq)Message comprising path computation information comprising routing andwavelength assignment (RWA) information and constraints from the PCC,wherein the first PCE receives a list of potential paths from a secondPCE that comprises private impairment data, wherein the first PCEestablishes IA-RWA based on the path computation information from thePCC and the potential paths from the second PCE, and wherein the PCEselectively transmits a RWA path reply that comprises the IA-RWA to thePCC.
 13. The network component of claim 12, wherein the RWA path replycomprises a message with a route, wavelengths assigned to the route, andan indicator regarding whether a corresponding path conforms to anoptical quality threshold.
 14. The network component of claim 12,wherein receiving path computation information from the PCC comprisesreceiving a RWA path re-optimization request that comprises a messagewith a path to be re-optimized and re-optimization options selected fromthe group consisting of re-optimizing the path while keeping the samewavelength(s), re-optimizing wavelength(s) while keeping the same path,and re-optimizing by allowing both wavelength and the path to change.15. The network component of claim 12, wherein receiving pathcomputation information from the PCC comprises receiving a combinedprimary and backup RWA request that comprises a message with wavelengthusage options selected from the group consisting of a same wavelength isrequired for primary and backup paths, and different wavelengths forprimary and backup paths are permitted.
 16. The network component ofclaim 12, wherein the processor is further configured to send a RWA-PCEto IV-PCE interface message indicating that more than one candidate pathbetween source and destination is requested and indicating a limit onthe number of optical impairment qualified paths to be returned by theIV-PCE.
 17. A method comprising: establishing, by the PCE, impairmentaware routing and wavelength assignment for a plurality of networkelements (NEs) in an optical network using routing and combinedwavelength assignment (WA) and impairment validation (IV); receiving, bya path computation element (PCE), a path computation element protocol(PCEP) Path Computation Request (PCReq) Message from a PCC, wherein thePCReq Message comprises an optical signal quality parameter thatindicates an impairment constraint that a computed path must meet topass an impairment validation optical quality check, and wherein the PCCdoes not comprise and is not positioned in a network management system;and performing, by the PCE, at least one operation selected from thegroup consisting of a Routing and Wavelength Assignment (RWA) pathrequest operation and a path re-optimization request operation, whereinthe RWA path request operation and the path re-optimization requestoperation each comprise calculating a path and performing an impairmentvalidation optical quality check on the calculated path.
 18. The methodof claim 17, wherein performing the RWA path request operation comprisestransmitting, by the PCE, a message with a path computation typeindicator, a path route, a wavelength assigned to the route, and anindicator that indicates whether the path has passed an optical qualitycheck.
 19. The method of claim 17 further comprising sending, by thePCE, a RWA-PCE to IV-PCE interface message indicating that more than onecandidate path between a source and a destination is requested andindicating a limit on the number of optical impairment qualified pathsto be returned by the IV-PCE.
 20. The method of claim 12, wherein thePCC does not comprise and is not positioned in a network managementsystem.